Tapped “P-traps” are an important safety feature in modern plumbing, and find their use for sewer, drain, and waste connections such as in floor drains, floor sinks and in commercial indoor fire sprinkler systems. Where a drain is connected to a sewer line, a tapped P-trap is used to ensure that sewer gas does not enter the building. Because the Uniform Plumbing Code (UPC) requires that all traps be primed, water must be supplied to the P-trap to keep the trap filled with water. The trap depends on being full of water to fulfill its function, and will not serve as a barrier to sewer gas if it goes dry.
In best practice, a “primer line” is joined to the trap at a tee and configured so that water flows into the trap at a slow drip, ensuring that the trap remains full. Access plates are arranged to permit maintenance access to a bleed valve that adjusts water flow into the trap, but the trap itself is frequently below slab and not accessible.
Typically, in a floor drain for example, a ½″ copper line is run through a series of solder joints to the “P-trap” and joins the cast iron at an adaptor which is provided with a ferrule to make a compression seal around the copper primer line. The layout of the primer line is typically more complex than wanted because conventional P-trap adaptors are in a fixed position on the trap pipe segment, so that the primer line must be brought to the adaptor rather than bringing the adaptor to the primer line. Plumbing is laid before the slab is poured, and best practice is to minimize turns in the piping and to avoid soft copper turns entirely because workers can kick, trip over or kink the plumbing lines when laying rebar or preparing the foundation, leading to slab leaks and other construction defects which are difficult and expensive to repair and result in potential liability that the plumber must insure against.
Wet “P-traps” also find use with floor sinks used in food preparation. The floor sink provides an air gap between a counter sink and the floor drain so that bacteria from the waste line cannot enter the sink if water backs up in the floor drain. Larger dish washers and sprinkler line pressure relief systems also use wet P-traps. A trickle of water, usually one drop every 10-20 sec, is used to continuously “prime” the trap so that gas remains confined underground. Thus there is a significant market for P-traps and associated fittings.
In commercial buildings, plumbing systems are typically assembled with cast iron pipe. Cast iron pipe is designed to be assembled by inserting a “spigot end” of a first pipe into a “hub end” of a second pipe and caulking to suppress leaks. Cast iron is not readily drilled out to accept a “tee” adaptor for admitting a primer line, and code does not permit use of the commonly available “BAP adaptors” when running cast iron line because of the difficulty in making proper seals to cast iron (BAP adaptors are intended to be glued in place). Gasketed “no-hub bands” are typically used to join cast iron pipe sections when making special connections. Tempting as it may be to simply join a plastic “tee” adaptor between caste iron stub ends using a band, this again poses the risk of damage during work on the foundation because any weight on the pipes is transferred to the weaker plastic adaptor, which can crack or deform at the joint. A “band” is the commonly used term for a gasketed sleeve, and is typically tightened in place using pipe clamps (sometimes termed “ring clamps”) provided with the sleeve. Bands are typically close-fitting and are supported by an external metal sheath or “shroud” seated under the pipe clamps so as to resist any unwanted motion of the pipes. However, bands do not permit the plumber to introduce a “tee” for making a connection to a primer line; the soft gasket would not support one.
Thus, there is a need in the art, for a plumbing coupling configured to permit joining of a primer line to a cast iron “P-trap” through a coupling tee, where the coupling overcomes the above disadvantages and weaknesses.